Belt tracking is a problem in any industry that uses conveyor belts. It is usually not a major problem but a maintenance nuisance that progressively becomes a major cost over a period of time.
Several variables affect belt tracking. The first and, perhaps most obvious, is misalignment of one or both conveyor end rollers. Misalignment of the rollers will cause corresponding belt tracking problems. Uneven tension applied to a belt can also result in tracking problems. Uneven tension will result in "stretching" of the belt on one side, thereby resulting in belt sides of unequal length. This also creates tracking problems. Uneven loading of conveyor belts also causes tracking problems as well as unequal driving forces across the belt width.
Numerous systems and concepts have been tried to eliminate persistent belt alignment problems.
Various conveyor belts have been developed over the years with design considerations relating to accurate tracking. Some belts will track better than others, but within any belt the ability to track varies considerably. This is due to the myriad of variables in the production of a belt. In order to produce a near perfect belt, the weave within the belt must be perfectly straight before the belt is coated or laminated. When the belt is cut for width, the cut must be straight with respect to the weave. Further, when the belt is cut to a desired length, the cut and lacing must be carefully executed to be square with the belt edges. If any of the above factors are off, the belt will track improperly.
Compounding this problem is the possibility of stretching the belt upon installation in order to correct for the manufacturing flaws. Overcorrection during initial tracking adjustments of the belt may result in stretching the belt in inappropriate areas. This may result in still further tracking problems. Undesired belt stretching may also be attributed to off-center loading.
Given the understanding that precision manufacture of belting is an impractical solution, and that activities such as improper loading, overcorrection, etc. may occur at any given time, there becomes a recognized need to provide some form of belt alignment correction that will compensate automatically for inappropriately constructed, mounted, and loaded belts.
Since it has been found that nearly any belt has a tendency to track improperly, the next solution attempted was to correct for the misalignment by periodically or consistently shifting the belt to an aligned, proper tracking orientation.
One attempt at the above solution is recognized in the crowned pulleys that have been commercially available for some time. A crowned pulley in a conveyor system will typically help belt tracking, if the belt is well constructed and used. Otherwise, the degree of crown on such pulleys is insufficient to influence proper tracking.
Another conventional attempt to correct for belt misalignment is the use of an angled snub roller. An angled snub roller can be used to overcome a belt tracking in a particular direction. Unfortunately, the influence of an angle snub roller depends on belt tension and load on the associated conveyor. If the load or belt tension changes, the belt position may correspondingly change unless scrupulous attention is made to adjustments with the snub roller.
Another attempt at assisting proper tracking of conveyor belts is the use of belt side guides. Plastic guide blocks are often used to confine an edge of a conveyor belt within the conveyor system. Unfortunately, pushing on the edge of the belt will not suffice to overcome the force of a misaligned belt, especially when the belt is under load. The blocks therefore help only to prevent major damage when "walk off" occurs.
Another attempt to overcome the above problems has been made in the belt drive system by lagging the drive pulley from the center out. This has favorable results over lagging from one side of the drive pulley to the other but is not a significant influence in belt tracking to avoid the adverse effects from poor belt construction or the tracking influences discussed above.
A combination of solutions has been attempted in certain conveyor belts which are now being designed with a "v"-belt laminated to the bottom center of the conveyor belt. The head pulley and tail pulley of the conveyor are then supplied with complementary "v" grooves to receive the "v"-belt.
The belt riding in these grooves forces the belt to stay in a centered, tracking orientation, as long as the "v"-belt is perfectly centered and in a straight line along the conveyor belt. Otherwise, the "v"-belt has a tendency to "climb" out of the "v" grooves and consequently stretch the belt in that area. Additionally, if lacing is not matched up correctly, the "v"-belt would not be lined up and would climb out of the grooves.
Furthermore, in wide belt applications, there is insufficient traction by a single "v"-belt to overcome any misalignment tendency that would occur along the broad frictional engagement between the head and tail rollers and the belt.
A more successful attempt has been made to provide an attachment to existing conveyors by which the return flight of the conveyor is trained over a pair of pivoted alignment rollers "midstream" between the head and tail conveyor rollers. These rollers are pivoted on one side of the conveyor in a selective manner by an air or hydraulic cylinder connected between the conveyor frame and the alignment rollers.
The cylinder may be selectively actuated to extend or retract, thereby swinging the alignment rollers to one side or the other of the pivot axis to affect tracking of the belt. This works well with the exception that the alignment rollers and carriage are quite bulky by nature and may not be used in confined places, especially with fairly short run conveyors.
All the pivotal motion of the alignment rollers is initiated from one side of the conveyor so the cylinder must have a significant stroke to accommodate for alignment problems to opposite sides of the head and tail rollers. This causes a problem, especially as indicated above, where the conveyor is to be used in confined quarters.
It therefor becomes clear that there remains a need for a compact yet effective system by which a conveyor belt may be selectively held in a prescribed aligned orientation with respect to head and tail rollers on a conveyor. The need is especially felt for such a device that will function in an effective manner to train belts of various width and length dimensions to operate along a prescribed path.